Sleep Rhythms

Sleep as a regular and naturally occurring altered state of consciousness that follows a circadian rhythm and involves the ultradian rhythms of REM and NREM Stages 1–4 sleep (excluding corresponding brain wave patterns and physiological responses for each stage

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Online Learning: SLIDE ICON GUIDE

What do you know about sleep?

What do you know about sleep?

Interesting facts

• What is the longest someone has slept?

If a coma counts…over 30 years

• What is the longest someone has gone without sleep?

18 days 21 hours and 10 mins

• Which animal sleeps the longest?

The brown bat = 19.9 hours a day

• Which animal sleeps the shortest?

The giraffe = 1.9 hours a day

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• Being awake for 17 hours is the equivalent of having a BAC of 0.05

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• Scientists are unable to explain a 1998 study that found when a bright light is shone at the back of your knees the sleep-wake cycle resets

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• You will spend approximately 27 years asleep

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• Ducks sleep with half an active brain to protect themselves from predators

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• Elephants stand during NREM but lie down for REM sleep

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Sleep as an ASC

Definition: A reversible behavioural state of perceptual disengagement from and unresponsiveness to the environment.

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A naturally and regularly occurring altered state of consciousness that follows an internally regulated daily cycle of about 24 hours and is characterised by a loss of conscious awareness.

• Sleep is an ASC
• Sleep occurs naturally
• Sleep involves progressing through different stages.
• Each stage has different levels of alertness and physiological responses.
• We spend approx ⅓ of our lives asleep

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Reversibility- A sleeper can always be awoken with a strong enough stimulus, such as noise or body contact

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Perceptual disengagement- The sleeper has no awareness of the sights, sounds, smells and other sensory stimuli in the external environment

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SC: Define sleep.

Characteristics of sleep as an ASC

Level of awareness: Very little awareness of our external environment

Content limitations: No conscious control of our thoughts. E.g we have strange dreams.

Controlled and automatic processes: Cannot perform other tasks.

Perceptual distortion: Attention to sensory stimuli is lowered, including pain.

Cognitive distortions: Disorganised and unrealistic thoughts during dreams.

Emotional Awareness: Emotions can be more or less intense during dreams e.g nightmare.

Self control: Lowered self control e.g we might snore or sleep talk.

Time Orientation: Ability to perceive time can be impaired.

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Physiological patterns of sleep

Through sleep our bodies shift through a number of stages

Each stage has its own unique physiological characteristics.

We use these characteristics to identify which stage of sleep someone is in. These characteristics include:

• Brainwaves
• Muscle tension
• Eye movement
• Body temperature
• Heart rate
• Blood pressure
• Respiration
• Hormone levels

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Biological rhythms

Biological rhythms are changes in body functions that repeat themselves through time in the same order.

Examples: Body temperature, blood pressure, blood sugar levels and sleep-wake cycle.

Each rhythm is maintained and controlled by an internal ‘biological clock’. This internal clock determines what time of day we are most alert, hungry, tired, hormones released ect.

This ‘clock’ is located in the hypothalamus

There are two types of rhythms

• Circadian (24 hours)
• Ultradian (less than 24 hours)

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Circadian Rhythm: Sleep-wake cycle

The sleep wake cycle is an example of a circadian rhythm.�

• A Circadian rhythm involves changes in bodily functions or activities that occur as part of a cycle with a duration of 24 hours�
• Despite it being internally produced the sleep-wake cycle is still influenced by environmental time-giving stimuli such as light/darkness, clocks, meal times, jobs and TV programmes.

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The sleep wake cycle is a daily cycle made up of time spent sleeping and time being awake and alert.

SC: Explain the concept of circadian and ultradian rhythms and provide examples of each.

Environmental cues are known as Zietgebers

Suprachiasmatic nucleus (SCN) and Melatonin

• An area of the hypothalamus called the suprachiasmatic nucleus (SCN) receives sensory information regarding the amount of light that has been detected by the eyes.
• Based on this information the hypothalamus sends a message to the Pineal gland to secrete more or less melatonin.
• Melatonin is a hormone that has sleep inducing qualities.
• This makes you feel tired when it is dark and helps stay awake during the day.

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SC: Explain the role of the SCN and melatonin in the sleep-wake cycle.

SC: Describe the relationship between light and melatonin.

Fun Fact: Cortisol gives you energy

Remember cortisol from stress?

It is released to give us energy during the Resistance stage.

Well just as melatonin is released at night to make you sleepy.

Cortisol is released in the mornings to help wake you up and give you energy and promote alertness.

Cortisol levels are highest in the morning and fall throughout the day.

1. Circadian rhythms last:
1. Approx 24hrs
2. Longer than 24hrs
3. Longer than 48hrs
4. Less than 24hrs
2. What is the most dominant circadian rhythm in humans?
3. Our internal body clock is found in the:
• Hypothalamus
• Thalamus
• Cerebral cortex
• amygdala
4. What part of the brain is responsible for the release of melatonin?
• Thalamus
• Hypothalamus
• Pineal gland
• Pituitary gland

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Ultradian Rhythms and NREM / REM sleep

An ultradian rhythm is a body rhythm that last less than 24 hours.

The sleep component of the sleep-wake cycle consists of ultradian rhythms. When we sleep we move between non-rapid eye movement (NREM) and rapid eye movement (REM).

On average one sleep cycle NREM/REM cycle last for 90 min.

Most adults experience 4-6 NREM/REM cycles per night.

The amount of time we spend in REM increases as the night goes on.

NREM accounts for 80% of our sleep

REM 20%

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SC: Differentiate between the sleep-wake cycle and a sleep cycle (as examples of circadian and ultradian cycles).

Sleep terms

• Sleep onset- The transition period from being awake to being asleep
• Sleep onset is often called a hypnagogic state

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• Sleep latency- The length of time it takes from being awake to being asleep.

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• Arousal threshold- The amount of stimuli it takes to wake someone up

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NREM AND REM SLEEP

• NREM sleep- non-rapid eye movement
• REM sleep- rapid eye movement

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• NREM and REM sleep periods

alternate throughout the night.

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Irregular cycling/absence of either sleep

state are associated with sleep disorders

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Definitions

• REM Sleep- A type of sleep that is characterized by brainwaves with high frequency and low amplitude. The muscles of the body are in a state of paralysis and dreams may be experienced. ��
• NREM Sleep- A type of sleep that is broken into four stages, where the sleeper falls into a deeper and deeper sleep as the stages progress. It is characterized by relaxation of the muscles, a slowing down of physiological functions and brainwaves that decrease in frequency and increase in amplitude

• The different stages of sleep and the corresponding sleep cycles are visualised using a hypnogram.
• A hypnogram is a sleep graph that tracks the proportion of time spent in each stage of sleep, including awakenings, throughout a sleep episode.

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When interpreting hypnograms, it is important to recognise that the stage of sleep is on the y axis and the duration of sleep is on the x axis.

The longer the line in the horizontal direction the greater the duration spent in a particular stage of sleep. To determine what this particular stage of sleep is,  align where the line is travelling in the horizontal direction with the vertical axis with the different stages of sleep.

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NREM vs REM SLEEP

• NREM SLEEP
• does not involve any rapid eye movement
• muscle movement as possible
• constitutes of approximately 80% of a sleep episode
• is subdivided into 4 distinct stages
• dreams are not usually recalled if woken up during during this stage

• REM SLEEP
• 20-25% of sleep time
• Bursts where the eyes move quickly beneath closed eyelids.
• Internally the body is more active than NREM e.g. increased heart rate.
• Muscles are very relaxed, very little movement.
• Paradoxical sleep: brain and body internally are active, but externally everything looks calm.
• REM sleep periods get longer as the night goes on.
• First cycle: 1-5 min, 2nd cycle: 12-15 min, 3rd 20-25 min.

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SC: Explain differences between REM and NREM sleep in terms of

• brainwave activity (frequency and amplitude)
• heart rate
• eye movements and
• muscle tension
• dreaming or non-dreaming
• purpose (mind vs body).

NREM: Stage 1

• Around 5 min.
• Can range from 30 sec - 10 min
• Transition from awake to asleep
• Losing awareness of our surroundings
• Light sleep we can easily wake from
• Enter a relaxed state (hypnagogic state)
• May experience hallucinations e.g. bright lights or images
• Hypnagogic jerks - involuntary muscle twitches that cause us to jolt.

NOTE: If woken in stage 1 we often don’t think we have been sleeping.

Physiological changes: A decrease in heart rate, respiration, body temperature and muscle tension, Hypnic jerk also experienced.

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• Describe a typical sleep episode (including timing of a sleep cycle, pattern of stages of sleep, and proportion of NREM vs REM).

NREM: Stage 2

• 10-25 min
• Can be easily woken
• Our body becomes more relaxed.
• Seen as the point where true sleep begins.
• Sleep 50% of sleep in stage 2.

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• Physiological changes: Body movements lessen, breathing enters a more regular rhythm, blood pressure and temperature fall, heart rate slows, eye movements stop.

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• Describe a typical sleep episode (including timing of a sleep cycle, pattern of stages of sleep, and proportion of NREM vs REM).

NREM: Stage 3

• Last from 3-10min
• The start of deep sleep
• Less responsive
• Difficult to wake
• If woken we feel disorientated.

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Physiological changes: Heart rate, blood pressure, body temp continue to drop, breathing is slow and steady.

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• Describe a typical sleep episode (including timing of a sleep cycle, pattern of stages of sleep, and proportion of NREM vs REM).

NREM: Stage 4

• In your first cycle you will spend 20-40 min in stage 4.
• As the night goes on less and less time is spent in stage 4, stage 4 sleep may disappear altogether from the cycle.
• Deepest sleep
• Very relaxed, little movement.
• Hardest to wake
• Overall 10-15% sleep time.

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• Physiological changes: Muscles completely relaxed, no eye movement, heart rate, blood pressure and body temp are at their lowest and most regular.

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• Describe a typical sleep episode (including timing of a sleep cycle, pattern of stages of sleep, and proportion of NREM vs REM).

REM Sleep

• 20-25% of sleep time
• Bursts where the eyes move quickly beneath closed eyelids.
• Muscles are very relaxed, very little movement.�
• Physiological changes: heart rate is faster and more irregular. Blood pressure rises, and breathing is quicker and more irregular. However, the sleeper looks totally relaxed�
• Paradoxical sleep: brain and body internally are active, but externally everything looks calm.
• REM sleep periods get longer as the night goes on.
• First cycle: 1-5 min, 2nd cycle: 12-15 min, 3rd 20-25 min.

• Describe a typical sleep episode (including timing of a sleep cycle, pattern of stages of sleep, and proportion of NREM vs REM).

Dreams and REM

• Most dreaming happens ( some dreaming can occur in NREM)
• If we are woken in REM we are likely to report we were dreaming.
• We often have 4-5 different dreams each night�
• Dreams in REM tend to follow a storyline and the dreamer often feels they are in a different world.
• The final REM period of the night is your final dream. This is often the longest, strangest and most exciting hence the one we often remember.
• In reality we remember few of our dreams

NOTE: NREM dreams are less vivid and less likely to be remembered.

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• What stage of sleep is this Good Boi likely to be in? Justify your  

Outline the pattern and proportions of NREM and REM sleep in a typical night’s sleep by a young adult. You may use a diagram (such as a chart or hypnogram) to support your description.

• Briefly describe the pattern and proportions of NREM and REM sleep in a typical night’s sleep for an adult.

• Describe a typical sleep episode (including timing of a sleep cycle, pattern of stages of sleep, and proportion of NREM vs REM).

Typical Night’s sleep for a healthy young adult

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Typical Pattern for adult - Cheat Sheet Notes

• a complete sleep cycle consists of a period of NREM sleep (but not necessarily all four stages) and a period of REM sleep�
• NREM and REM periods alternate e.g. NREM, REM, NREM etc.�
• a complete sleep cycle has a duration of about 90 minutes�
• about 5–6 cycles per night (depending on sleep episode duration)�
• later sleep cycles tend to be longer-lasting
• about 75–80% NREM and 20–25% REM �
• NREM occurs in stages from 1–4, then back from 4 to 1, but often missing one or more stages, especially stage 1�
• deepest sleep tends to occur in the first third of the night i.e. stages 3 and 4 tend to predominate in NREM sleep during the first half of the sleep episode, particularly in the first two cycles. As the night progresses, stage 2 begins to account for the majority of NREM sleep, and stages 3 and 4 may disappear.�
• NREM period shortens and REM period lengthens as the night progresses (with REM sleep periods closer together and longest in the last third of the night)�
• brief episodes of wakefulness tend to occur in later cycles, generally in association with transitions between stage 2 and REM sleep.

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Success Criteria

• Define sleep.
• Explain the concept of circadian and ultradian rhythms and provide examples of each.
• Explain the role of the SCN and melatonin in the sleep-wake cycle.
• Describe the relationship between light and melatonin.
• Describe some behaviours you might be engaging in that affect your sleep-wake cycle due to light.
• Explain the role of melatonin in maintaining the sleep-wake cycle.
• Explain how the how the sleep-wake cycle can be influenced by external factors (zeitgebers).
• Provide examples of zeitgebers that influence you in your everyday life.
• Differentiate between the sleep-wake cycle and a sleep cycle (as examples of circadian and ultradian cycles).
• Explain similarities between REM and NREM sleep in terms of reversibility, perceptual disengagement, unresponsiveness.
• Explain differences between REM and NREM sleep in terms of
• brainwave activity (frequency and amplitude)
• heart rate
• eye movements and
• muscle tension
• dreaming or non-dreaming
• purpose (mind vs body).
• Describe a typical sleep episode (including timing of a sleep cycle, pattern of stages of sleep, and proportion of NREM vs REM).